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IQ and schizophrenia in a Swedish national sample: their causal relationship and the interaction of IQ with genetic risk.

ABSTRACT: The authors sought to clarify the relationship between IQ and subsequent risk for schizophrenia.IQ was assessed at ages 18-20 in 1,204,983 Swedish males born between 1951 and 1975. Schizophrenia was assessed by hospital diagnosis through 2010. Cox proportional hazards models were used to investigate future risk for schizophrenia in individuals as a function of their IQ score, and then stratified models using pairs of relatives were used to adjust for familial cluster. Finally, regression models were used to examine the interaction between IQ and genetic liability on risk for schizophrenia.IQ had a monotonic relationship with schizophrenia risk across the IQ range, with a mean increase in risk of 3.8% per 1-point decrease in IQ; this association was stronger in the lower than the higher IQ range. Co-relative control analyses showed a similar association between IQ and schizophrenia in the general population and in cousin, half-sibling, and full-sibling pairs. A robust interaction was seen between genetic liability to schizophrenia and IQ in predicting schizophrenia risk. Genetic susceptibility for schizophrenia had a much stronger impact on risk of illness for those with low than high intelligence. The IQ-genetic liability interaction arose largely from IQ differences between close relatives.IQ assessed in late adolescence is a robust risk factor for subsequent onset of schizophrenia. This association is not the result of a declining IQ associated with insidious onset. In this large, representative sample, we found no evidence for a link between genius and schizophrenia. Co-relative control analyses showed that the association between lower IQ and schizophrenia is not the result of shared familial risk factors and may be causal. The strongest effect was seen with IQ differences within families. High intelligence substantially attenuates the impact of genetic liability on the risk for schizophrenia.

SUBMITTER: Kendler KS

PROVIDER: S-EPMC4391822 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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IQ and schizophrenia in a Swedish national sample: their causal relationship and the interaction of IQ with genetic risk.

Kendler Kenneth S KS Ohlsson Henrik H Sundquist Jan J Sundquist Kristina K

The American journal of psychiatry 20141107 3

<h4>Objective</h4>The authors sought to clarify the relationship between IQ and subsequent risk for schizophrenia.<h4>Method</h4>IQ was assessed at ages 18-20 in 1,204,983 Swedish males born between 1951 and 1975. Schizophrenia was assessed by hospital diagnosis through 2010. Cox proportional hazards models were used to investigate future risk for schizophrenia in individuals as a function of their IQ score, and then stratified models using pairs of relatives were used to adjust for familial clu ...[more]

PMID: 25727538

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Project description:ImportanceFamily and genetic approaches have traditionally been used to evaluate our diagnostic concepts. Using a novel method, the family genetic risk score (FGRS), can we validate the genetic architecture of major affective and psychotic disorders in a national Swedish sample?ObjectiveTo determine whether FGRSs, calculated for the entire Swedish population, can elucidate the genetic relationship between major affective and psychotic disorders and clarify the association of genetic risk with important clinical features of disease.Design, setting, and participantsThis cohort study included the native Swedish population born from January 1, 1950, through December 31, 1995, and followed up through December 31, 2017. Data were collected from Swedish population-based primary care, specialist, and hospital registers, including age at first registration for a psychiatric diagnosis and number of registrations for major depression, bipolar disorder, and schizophrenia. Data were analyzed from October 15, 2020, to February 2, 2021.ExposuresFGRSs for major depression, bipolar disorder, and schizophrenia calculated from morbidity risks for disorders in first- through fifth-degree relatives, controlling for cohabitation.Main outcomes and measuresDiagnoses of major depression, bipolar disorder, schizophrenia, schizoaffective disorder, and other nonaffective psychoses (ONAPs), age at registration, and number of registrations for major depression, bipolar disorder, and schizophrenia. Diagnostic conversion of major depression to bipolar disorder and ONAPs to schizophrenia was assessed by Cox proportional hazards regression models.ResultsThe cohort included 4 129 002 individuals (51.4% male) with a mean (SD) age at follow-up of 45.5 (13.4) years. Mean FGRSs for major depression, bipolar disorder, and schizophrenia produced distinct patterns for major depression, bipolar disorder, schizophrenia, schizoaffective disorder, and ONAPs with large separations between disorders. In major depression, bipolar disorder, and schizophrenia, high FGRSs were associated with early age at onset and high rates of recurrence: a high mean FGRS for bipolar disorder was associated with early age at onset (younger than 25 years, 0.11; 95% CI, 0.11-0.12) and higher recurrence (8 or more registrations, 0.11; 95% CI, 0.11-0.12) in major depression. The schizophrenia FGRS was separately associated with psychotic and nonpsychotic forms of major depression (0.10; 95% CI, 0.06-0.14 vs 0.03; 95% CI, 0.02-0.03) and bipolar disorder (0.22; 95% CI, 0.16-0.28 vs 0.11; 95% CI, 0.09-0.12). The bipolar disorder and schizophrenia FGRSs were associated with conversion from major depression to bipolar disorder (eg, hazard ratio, 1.70 [95% CI, 1.63-1.78] for high vs low bipolar FGRS) and ONAP to schizophrenia (eg, hazard ratio, 1.38 [95% CI, 1.27-1.51] for high vs low schizophrenia FGRS).Conclusions and relevanceIn this Swedish cohort study, the FGRSs for major depression, bipolar disorder, and schizophrenia for the Swedish population clearly separated major affective and psychotic disorders from each other in a larger and more representative patient sample than previously possible. These findings provide possible validation, from a genetic perspective, for these major diagnostic categories. These results replicated and extended prior observations on more limited samples of the association of FGRS with age at onset, recurrence, psychotic subtypes, and diagnostic conversions.

Project description:ObjectiveThe objective of this study was to clarify the etiology of substance-induced psychotic disorder and its progression to schizophrenia in a Swedish national sample.MethodsIndividuals with a registration of substance-induced psychotic disorder between 1997 and 2015 in national medical registries (N=7,606) were followed up for a mean of 84 months. Data from medical, criminal, and pharmacy registries on first-degree through third-degree relatives were used to calculate familial risk scores for nonaffective psychosis, drug abuse, and alcohol use disorder.ResultsIndividuals with substance-induced psychotic disorder had large elevations in standardized familial risk scores for drug abuse (+1.09, 95% CI=1.02, 1.15) and alcohol use disorder (+0.98, 95% CI=0.93, 1.03) and modest elevations for nonaffective psychosis (+0.35, 95% CI=0.30, 0.41). The cumulative risk for progression to schizophrenia was 11.3%; it was lowest for alcohol-induced and highest for cannabis-induced psychotic disorder, and it was predicted by early age at diagnosis of substance-induced psychotic disorder, male sex, and further registrations for episodes of drug abuse, alcohol use disorder, and substance-induced psychotic disorder. A risk prediction model found that 47% of individuals who converted to schizophrenia were in the upper 20% of risk. Familial risk scores for drug abuse and alcohol use disorder did not significantly discriminate those who converted to schizophrenia from those who did not, while familial risk score for nonaffective psychosis did (0.67, 95% CI=0.40, 0.95, versus 0.33, 95% CI=0.28, 0.39). Familial risk scores for nonaffective psychosis were indistinguishable between individuals with schizophrenia with and without prior substance-induced psychosis. Assignment of early retirement by the Swedish Social Insurance Agency strongly discriminated between individuals with substance-induced psychotic disorder with and without later schizophrenia.ConclusionsSubstance-induced psychotic disorder appears to result from substantial drug exposure in individuals at high familial risk for substance abuse and moderately elevated familial risk for psychosis. Familial risk for psychosis, but not substance abuse, predicts progression from substance-induced psychosis to schizophrenia. Schizophrenia following substance-induced psychosis is likely a drug-precipitated disorder in highly vulnerable individuals, not a syndrome predominantly caused by drug exposure.

Project description:IntroductionSleep is associated with psychiatric disorders. However, their causality remains unknown.MethodsThe study explored the causal relationship between seven sleep parameters (sleep duration, insomnia, sleep apnea, chronotype, daytime dozing, napping during the day, and snoring) and three psychiatric disorders including major depressive disorder (MDD), schizophrenia, and attention-deficit/hyperactivity disorder (ADHD) using two-sample Mendelian randomization (MR). Genome-wide association study (GWAS) summary data for sleep parameters were obtained from the United Kingdom biobank, FinnGen biobank, and EBI databases. MR-Egger, weighted median, inverse-variance weighted (IVW), simple mode, weighted mode, maximum likelihood, penalized weighted median, and IVW(fixed effects) were used to perform the MR analysis. The heterogeneity was detected by Cochran's Q statistic. The horizontal pleiotropy was detected by MR Egger. The sensitivity was investigated by the leave-one-out analysis.ResultsInsomnia (OR = 2.02, 95%CI = 1.34-3.03, p = 0.001, False-discovery rate (FDR) corrected p-value = 0.011) and napping during the day (OR = 1.81, 95%CI = 1.34-2.44, FDR corrected p-value<0.001) were associated with an increased risk of MDD. Longer sleep duration (OR = 2.20, 95%CI = 1.24-3.90, FDR corrected p-value = 0.049) had an association with the increased risk of schizophrenia, while daytime dozing (OR = 4.44, 95%CI = 1.20-16.41, corrected p-value = 0.088)and napping during the day (OR = 2.11, 95%CI = 1.11-4.02, FDR corrected p-value = 0.088) had a suggestive association with an increased risk of schizophrenia. Longer sleep duration had a suggestive association with a decreased risk of ADHD (OR = 0.66, 95%CI = 0.42-0.93, FDR corrected p-value = 0.088).ConclusionThis study provides further evidence for a complex relationship between sleep and psychiatric disorders. Our findings highlight the potential benefits of addressing sleep problems in the prevention of psychiatric disorders.

Dataset Information

IQ and schizophrenia in a Swedish national sample: their causal relationship and the interaction of IQ with genetic risk.

Publications

IQ and schizophrenia in a Swedish national sample: their causal relationship and the interaction of IQ with genetic risk.

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